The present invention relates generally to sewage systems, and more particularly, to sewage systems which utilize differential air pressure to create flow therein, and have inlet vacuum valves with a tapered plunger to prevent valve jamming and subsequent air leakage as the vacuum seal is impaired.
Sewage systems initially were gravity operated, including a network of underground pipes leading from various sources of waste (e.g., homes, businesses, etc.) to a sewage treatment plant. However, irregular terrains and distances posed between the entry and collections points of the waste significantly limited the ability to dig deep trenches to provide a continuous, downhill flow of sewage. Thus, mechanical pumps were placed at strategic points along the pipe network to provide a positive force behind waste flowing in a more-shallowly laid piping network. In actuality, though, pressure pumps were needed at every sewage input point for such a system.
Vacuum-operated systems were proposed as an alternative, as exemplified by U.S. Pat. No. 3,115,148 issued to S.A.J. Liljendahl. The Liljendahl patent describes a vacuum system which uses two separate piping networks to carry different effluent streams. While the waste products from bathtubs, wash basins, sinks, etc. (gray water), are conveyed by a conventional gravity system, waste products discharged from water closet bowls, urinals, and similar sanitary apparati (black water) are transported by a separate, vacuum system. The conduits in the latter system are provided with "pockets" in which sewage is collected so as to form a plug which entirely fills the cross-sectional area of the pipe and effects conduit closure. A plug of sewage is moved by a pressure differential force along a conduit in an integral condition. The kind of vacuum-operated system taught by the Liljendahl patent is called "plug flow."
U.S. Pat. No. 3,730,884, issued to B. C. Burns et al., describes a sewage system using "vacuum-induced plug flow" in which both black water and gray water are handled by a single piping system. A "coherent plug" of sewage is transported by a vacuum pressure differential through a pipe for a short distance. The plug will disintegrate, however, as it moves through the pipe due to friction and other forces, resulting in a diminishment of the pressure differential moving the plug. Therefore, a series of plug reformers, which in their simplest form may be a dip or pocket in the pipe, serve as a trap for sewage and aid in the reformation of a coherent plug. The pockets are designed so that sewage entirely fills the pipe bore. Operation of the system requires that the plug of sewage seal the pipe bore. This process of alternate plug disintegration and reformation continues until the sewage eventually passes completely through the pipe. The pressure differential for each of these plugs is less than the total available system pressure differential because of the serial arrangement of the plug pockets in a pipe.
U S Pat. No. 4,179,371, issued to B. E. Foreman et al., describes an apparatus and method for transporting sewage from a source of sewage to a collection means. A pressure differential is maintained in the piping between the source and the collection means. Sewage is transported through the conduit in the form of a generally hollow cylinder. When no sewage is being transported, the residual sewage retained in the conduit generally does not close the conduit and permits the same pressure to be maintained throughout the conduit. Injection means are provided, which may be a valve opened in response to a predetermined condition. The conduit is laid out in a saw-toothed configuration with a riser portion, a downslope portion, and a low point portion in which residual sewage not discharged from the system may collect. The residual sewage is generally insufficient to close the conduit, thereby permitting communication of the same pressure throughout the conduit. Thus, the apparatus, as disclosed by Foreman, may include a gravity-fed sewage collection tank at atmospheric pressure having its contents intermittently injected into a vacuum-pressurized conduit laid out in saw-toothed fashion, which permits full vacuum to be communicated throughout the conduit under typical operating conditions.
U.S. Pat. No. 3,807,431, issued to S. A. A. Svanteson, describes a device for conducting waste liquid from a receptacle tank to a pneumatic liquid disposal system. The device includes a vacuum valve, consisting of a wye-body conduit with a diaphragm defining an upper housing. A spring biases the diaphragm against the valve stop of the conduit to close the valve and produce a seal. However, because a portion of the bottom side of the diaphragm is in communication with the vacuum pressure condition existing in the downstream portion of the conduit while the valve is closed, when the same vacuum pressure condition is introduced to the upper chamber, there will be little pressure differential to move the diaphragm in an upwards direction and, indeed, any pressure differential must overcome the downward, positive force exerted by the spring. Thus, if the control valve does open in response to the application of differential pressure, it only will do so partially, which promotes blockage of the valve as the waste liquid passes through. In general, the vacuum valve as taught by Svanteson will not open fully until the waste liquid has already passed by and air at atmospheric pressure is subsequently transported through the valve and conduit. This condition of partial opening of the control valve is an inherent problem with Svanteson, which can deleteriously affect the operation of the vacuum sewerage transport system.
U.S. Pat. No. 4,171,853, issued to D. D. Cleaver et al., describes a general structure and method of operation of a vacuum valve device for sealing and unsealing the conduit at the point of injection of sewage into the system. A controller assembly is attached to the valve. Once the valve opens in response to a signal received from the controller unit, accumulated sewage flows into the vacuum sewerage system to a remote collection station for subsequent transfer to a facility. These vacuum valves are closed to seal the vacuum system from atmospheric pressure by allowing atmospheric pressure to enter the internal upper housing chamber of the vacuum valve in response to a signal from the associated control unit to cause the closing of a rigid, plastic, internal plunger located within a centrally disposed valve chamber. Movement of the plunger is aided by an internal spring member located inside the upper housing of the valve unit. The plunger, as taught by Cleaver, is usually cylindrical in shape and operatively connected to the lower end of a piston driving member positioned against the spring.
The use of a cylindrically-shaped plunger head, however, presents a number of problems. Small stones, chips, and other solid particles are present in the various connecting pipes within the vacuum sewerage system. Yet, the physical clearance between the rigid cylindrical plunger and the wall of the vacuum valve chamber is sufficiently large that small stones, chips, solid particulate matter, rags, etc. can lodge between the valve chamber wall and the plunger as the waste matter is transported during operation of the system. Occasionally, this causes the cylindrical plunger to be jammed against the wall of the internal valve chamber while the vacuum valve is being pulled to the "open" position. Not only is the plunger damaged, but also the vacuum valve cannot be properly closed again in response to the signal from the controller unit. This condition results in continuous air and fluid leakage through the partially open vacuum valve and improper operation of the valve. Moreover, the leaking air and fluid will impair efficient operation of the overall vacuum transport system by destroying the pressure differential within the conduit downstream from the partially open valve. Proper operation of the system may only be restored once maintenance personnel identify which of the numerous valves have failed and service each one of those valves, a time consuming and cumbersome job.
Furthermore, under repetitive vacuum cycling, the rubber seat at the end of the plastic, cylindrical plunger, which physically engages the internal valve stop of the wye-body conduit pipe when the vacuum valve is in the "closed" position, tends to be pulled away from the end of the cylindrical plunger as the vacuum valve is opened. This allows small stones, chips, and other solid particles to become lodged between the rubber seat and the end of the plastic cylindrical plunger. This condition interferes with proper closure of the vacuum valve, thereby causing leakage when the valve is in the "closed" position.
The internal valve stop of the wye-body conduit pipe, as shown in the vacuum valve of the prior art, is positioned adjacent to, and below, the rubber seat at the end of the plastic cylindrical plunger, and will occasionally leak, thereby permitting unwanted air and fluid leakage into the system. In addition, because of the tight tolerance required between the internal valve stop of the wye-body and the rubber seat at the end of the cylindrical plunger, slight deviations in the angle of machining of the valve stop causes the cylindrical plunger incorrectly to engage the opposed valve stop of the wye-body. Thus, this incorrect seating can become yet another source of air and fluid leakage from the sump holding the accumulated waste liquid in the vacuum main.
And finally, the prior art vacuum valves have experienced leakage through the seal surrounding the operating shaft of the valve piston. This seal is provided between the internal valve chamber and lower housing chamber of the vacuum valve, preventing liquid or pressure communication therebetween. Leakage into the lower housing chamber permits fluid contamination into the control unit for the inlet vacuum valve by way of a connector tube which joins these two elements in common to an atmospheric air vent. This seepage damages the individual control unit over time. To the extent that sewage contamination leaks into the lower housing chamber of the vacuum valve, or into the associated control unit, maintenance of the vacuum valve is exacerbated, and system reliability is impaired.
All of these various problems with the proper operation of the vacuum valves of the prior art prevent "positive closure" of the valve by which the rubber seat attached to the plunger engages firmly with the internal valve stop of the wye-body conduit pipe in order to create an air-tight seal to promote a pressure differential across the valve and maintain a vacuum pressure condition downstream of the valve. Moreover, they cause labor costs associated with locating, servicing, and repairing damaged valves. Furthermore, the most expedient way to correct damaged cylindrical plungers is to remove and replace the entire vacuum valve, complicated by the fact that the valves and conduit lines are laid many feet below ground level. Any fluid contamination leaking into the vacuum valve will only increase these costs of repair.